The present invention relates to improvement of a lead frame carrying method and a lead frame carrying apparatus.
A die bonding step of mounting a die to a lead frame is performed by applying a bond to a predetermined portion of the lead frame positioned on a pair of carrier rails and mounting the die on the bond. As a preprocessing step, the lead frame mounted on a magazine is moved and mounted onto the carrier rails. The lead frame mounted on the carrier rails is carried to a dispenser side.
The lead frame which has completed die bonding is carried to a next step along the carrier rails.
A unit (mechanism) for holding the lead frame during carrying will be described below with reference to the drawings.
FIG. 4 is a view showing an appearance of the lead frame, and FIG. 5 is a sectional view showing a structure of lead frame holding means in a lead frame carrying apparatus according to the prior art.
In FIG. 5, a unit 1 serves to clamp a side edge portion 2a of a lead frame 2. As shown in FIG. 4, the lead frame 2 has a plurality of pin holes 101 provided in a line on right and left side edge portions. In FIG. 4, the number of the pin holes 101 is five. A pin (not shown) is inserted into the pin holes 101 to determine right and left positions of the lead frame 2 at a step after the die bonding step.
The reference numeral 3 denotes a solenoid supported on a unit box 4, and the reference numeral 5 denotes a plunger of the solenoid 3. A tip portion of the plunger 5 comes in contact with an upper left portion of a swing lever 6. The swing lever 6 is supported clockwise (in a direction of an arrow .theta.1) or counterclockwise (a direction of an arrow .theta.2) on the unit box 4 by a pivot section 7 so as to freely swing.
The reference numeral 8 denotes a receiving plate attached to the unit box 4 such that an upper face thereof is on a level with an upper face 9e of a carrier rail 9b, the reference numeral 10 denotes a spring having a lower end attached to the receiving plate 8 and an upper end attached to a lower left portion of the swing lever 6, and serves to energize the lower left portion upward. A lower right portion of the swing lever 6 is hooked downward.
When the solenoid 3 is caused to operate in such a direction as to pull the plunger 5, a tip portion 6a of the swing lever 6 is rotated clockwise (in the .theta.1 direction) by force of the spring 10. A side edge portion of the lead frame 2 is pressed downward by the tip portion 6a. Consequently, the side edge portion 2a of the lead frame 2 is clamped between the tip portion 6a of the swing lever 6 and the receiving plate 8.
When the operation of the solenoid 3 is released, the plunger 5 is extended to its original length against the force of the spring 10 so that the swing lever 6 swings counterclockwise (in the .theta.2 direction). Consequently, the clamping state of the side edge portion 2a of the lead frame 2 is released.
In recent years, nickel (Ni) and palladium (Pd) or Ni, Pd and gold (Au) are laminated and plated over a whole periphery of a copper (Cu) lead frame as shown in FIGS. 6 (a) and 6 (b).
Such a lead frame has a surface which is much smoother than that of a Fe lead frame (a so-called "42 alloy") according to the prior art. During carrying, the lead frame cannot surely be clamped. For this reason, yield is deteriorated at the die bonding step.
In the case where the lead frame has a top layer plated with a gold layer, the gold layer on a back face of the lead frame is easily damaged by coming in contact with a pair of carrier rails in the process of carrying the lead frame along the carrier rails because the gold layer is soft. Therefore, a finished product is affected. Furthermore, the gold layer on the back face of the lead frame is scraped due to contact with the carrier rails so that fine "refuse" is generated. This refuse sometimes blocks the pin hole 101. When the pin hole 101 is blocked, the lead frame cannot be positioned well at a step after the die bonding step. Therefore, it is also necessary to stop the apparatus in order to ensure normal operation. Consequently, an operation rate of the apparatus is reduced.